Antigen test by their name mean a procedure to detect or measure specific protein as antigen or antibodies in blood or fluid.
They are taken by swabbing nasal or throat cavity to detect a specific protein (SARS-CoV-2 nucleocapsid protein) that is part of Coronavirus. Some antigen tests use tester’s saliva to detect the protein. This protein is sought in an infected person as it is the most abundant protein that Covid-19 virus carries. Antigen tests tend to be more effective when tested serially, meaning a person has to take the same test (brand/manufacturer) few times in a single week span. Antigen tests work best when you show symptoms of Covid-19.
What are the potential risks and benefits of Antigen testing?
• Possible discomfort or other complications that can happen during sample collection
• Possible incorrect test result
• Results may help limit the spread of Covid-19 to your family and those you come in close contact with
• Results along with other information, can help your healthcare provider make informed recommendations about your care.
Molecular or PCR tests
This method of testing in a lab or point of care facility works by directly detecting viral nucleic acid in blood or samples taken from mucus from inside the nose or back of the throat, which means fragment of the RNA of the virus is taken and amplified(copied) many times (billions). This is done by taking two short DNA primers that are designed to bind to the start and end of the DNA target. Then the DNA from the virus is added and placed in a PCR (Polymerase chain reaction) machine.
The PCR machine increases and decreases the temperature while mixing until all three DNA strands bind together to form synthetic DNA. This is also called Nucleic Acid Amplification Test (NAAT). This amplification of specimen helps it detect small amounts of SARS-CoV-2 making it a more reliable and most sensitive method of testing.
There are many different methods of NAATs that tests use namely:
• Nicking endonuclease amplification reaction (NEAR)
• Transcription mediated amplification (TMA)
• Loop-mediated isothermal amplification (LAMP)
• Helicase-dependent amplification (HDA)
• Clustered regularly interspaced short palindromic repeats (CRISPR)
• Strand displacement amplification (SDA)
Advantages of PCR testing
• Valuable for detecting specific pathogens that are difficult to culture in vitro or require a long cultivation period
• Significantly more rapid in providing results compared to culturing
• Valuable screening tool
Limitations of PCR testing
• PCR testing alone may be limited as a diagnostic tool
Antibody test or Serologic test
Antibody test unlike PCR do not detect any pathogens, but instead their immune response to their presence. If a person is infected with Covid-19, the antibody test tries to detect the presence of any antibody generated by the person’s immune system.
The antibodies are usually detected 1 to 2 weeks after the onset of infection. Antibody test are not very useful in the early course of the illness. Post Covid and Long Covid will show better results using this Antibody test. These tests have shown to be specific to particular strain of Covid-19 for which they were designed for, Pan Covid Antibody tests have not been developed yet. Since there isn’t much data about the efficacy of antibody test on different strains of Covid-19 it is difficult to tell their benefits.